Telephone system



July 18, 1939. I TAYLOR ET AL 2,166,329

TELEPHONE SYSTEM Filed Jan. 28, 1937 2 Sheets-Sheet 1 FIG. 1

FROM PRECEDING 5 WI TC H INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER ATTORNEY.

July 18, 1939.

R. TAYLOR ET Al.

Filed Jan. 28, 1937 TELEPHONE SYSTEM h He. 2

5U55EOUENT SWITCH b 1 W wwwl0 I SWITCH INVENTORS REGINALD TAYLOR GEORGE 77-!0MA5 BAKER ATTORNEY.

2 Sheets-Sheet 2 Patented July 18, 1939 UNITED STATES PATENT OFHQE TELEPHONE SYSTEM Application. January 28, 1937, Serial No. 122,728 In Great Britain January 29, 1936 Claims.

The present invention relates to automatic switches of the type used in telephone or like systems and is more particularly concerned with an improved circuit arrangement for securing better performance of certain of the controlling relays therein. In general such switches are provided with an impulse accepting relay which responds to at least one train of impulses and controls a so-called guard relay which maintains the circuit in an operative condition while the impulses are being received. Usually this guard relay is provided with a copper collar or so-called slug on its core with the object of making it sufficiently slow to release so that it holds between successive 15 impulses of a train. As will be appreciated however this copper collar takes up an appreciable proportion of the available winding space with the result that power is lost and the ability of the relay to carry a heavy spring load is impaired. Arrangements have already been proposed whereby this loss of power may be avoided by dispensing with the copper collar and providing a fully wound coil which is arranged to be short-circuited between successive impulses in order to achieve the required slugging eifect. Such arrangements were not found to be entirely satisfactory however, mainly due to the fact that from practical considerations the short-circuiting of the guard relay and the impulsing of the magnet had to be controlled from the same armature of the impulse accepting relay with the result that the circuits of the uard relay and the magnet became interconnected in such a way that the latter was seriously shunted and its operating speed was reduced.

The chief object of the present invention therefore is to provide an improved circuit arrangement of the type described in which the guard relay and driving magnet are interconnected in such manner that the magnet is not appreciably slowed during its release.

According to the invention the 'guard relay is energised from a separate non-inductive battery feed when the impulsing relay first energises and the magnet is subsequently connected in parallel with the said feed so as to be energised by the short-circuiting of the guard relay each time the impulsing relay releases, the battery feed for the guard relay including a rectifier which prevents the operation of the magnet being prejudiced thereby.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. 1 and 2.

These should be arranged side by side to form a complete circuit and show the invention applied to a vertical and rotary switch of the mechanical construction disclosed in Patent No. 2,028,689, issued to R. N. SaXby on January 21, 1936, which switch is arranged to have two sets of wipers each having access to 100 outlets.

Considering now the detailed operation of the circuit, when the switch is taken into use the loop placed across its incoming negative and positive conductors operates relay A over its upper and lower windings and armature a! operates relay B in series with the metal rectifier MBA which is in a conductive direction. Relay B upon operating, at armature b3 connects a guard earth to the release trunk conductor P, at armature bi completes a locking circuit for itself, at armature b4 energises relay C over its upper winding in series with resistance YA and at armature bl lights the supervisory lamp LP which is connected to battery over common conductor ie by way of common equipment which is arranged to give an alarm if the switch fails to step off-normal and open the springs N3 within a predetermined period. If the switch is functioning as a first selector the middle winding of relay A is connected to earth at armature b6 by way of a dial tone transformer over common conductor l2 so that tone is applied to the incoming speaking leads in a balanced circuit by induction from the middle winding of relay A to the two outer windings so as: to inform the calling subscriber that he may commence dialling. Relay C at armature c i prepares a circuit for the vertical magnet VM which however is non-operative in series with the winding of relay B.

When the first series of impulses is received, relay A responds and each time it releases a circuit is completed to energise the magnet VM as follows: earth, armatures bl and at, rotary oifnormal contacts NR3, armature c l, low resistance lower winding of relay C, vertical magnet VM to battery, and accordingly the switch wipers are stepped by the vertical magnet to the desired level. During the impulse train it will be noticed that relay B is intermittently short-circuited by the resting armature at but this relay will remain held due to the slugging effect of the short-circuiting. The presence of the metal rectifier MBA in the energising circuit of relay B prevents the slowing down of the vertical magnet operation which would otherwise result due to the connection of a comparatively low value noninductive resistance in parallel with its winding. It will be readily understood that neither the vertical magnet nor relay C will hold in series with relay B and moreover the inductance of the latter relay is such that it has no appreciable effect on the performance of the magnet.

On the first vertical step the off-normal springs are mechanically operated and at contacts NI a circuit is completed from earth, armature b3, contacts NR4, armature 03, contacts rm, contacts NI and armature 175 to operate relays HA and HB in parallel over their middle windings, while springs N3 extinguish the supervisory lamp LP. Relays HA and H13 upon operating connect their right-hand windings to the testing wipers P2 and PI respectively while a circuit is completed from earth over armatures ha2 and hbI to short-circuit the upper winding of relay C and the slugging effect thus produced enables this relay to hold satisfactorily during the train of impulses received.

At the end of the train of impulses relay A remains steadily operated and after a short period relay C releases and completes a self-interrupted driving circuit for the rotary magnet RM from earth, armature b3, armatures 71.171 and M11, rotary magnet interrupter contacts rm, contacts NI and 02 to battery via the magnet RM. On the first energisation of the magnet the wipers will be advanced into engagement with the first set of contacts in the level selected whereupon the rotary off normal springs are mechanically operated. The magnet interrupter contacts rm will also be opened.

If the outlets encountered by both the PI and P2 wipers are engaged, that is, if they are marked by the presence of earth or booster battery metering potential on the test contact, relays HB and HA will both be maintained operated over their right-hand windings and the disconnection of their initial operating circuits over their middle windings by the interrupter contacts rm is therefore without effect. However, the rotary magnet RM which is connected in parallel with these relays releases and when the interrupter contacts again close the magnet is re-energised to advance the wipers on to the next set of contacts. This stepping operation continues automatically till a free outlet is found or alternatively the wipers are advanced to the 11th position.

Assuming that the wiper P2 is the first to encounter a free outlet, that is, one unmarked by earth or booster battery potential, relay HA will quickly restore and at armature haI open the rotary magnet driving circuit while the selected outlet is immediately busied from earth over armatures b3, hafi and M12. Relay HB however will remain held from the busy marking potential picked up by the wiper PI. At armature ha2 the short circuit is now removed from the upper winding of relay C and this relay immediately re-operates and at armatures c5 and c6 switches the speaking leads through by way of armatures ha3, hb3 and hbfl to the lower set of negative and positive wipers. The A and B relays are now operated in the succeeding switch and return a guarding and holding earth potential over the P wire which is extended by Way of armatures M22 and M16 on to the release trunk conductor P. An alternative holding circuit is now provided for relay HB by way of the earthed release trunk, armatures hb'l and M1, left-hand winding of relay HB, contacts NR3, and armature 04, to battery via the lower winding of relay C in series with the magnet VM (non-operative in this condition). Relay C also releases relay A since contacts NRI and NR2 are now open and relay A at armature aI short circuits and releases relay B.

If, however, the PI wiper is the first to encounter a free outlet, relay HB releases to open the magnet driving circuit at armature hb'I while the outlet selected is immediately guarded from earth, armatures b3 and M25, contacts S2 and armature b'I. Relay HB upon releasing, at armature hb2 also releases relay HA while the shortcircuit is removed from relay C as before. Upon the operation of relay C as previously described relay HA will be re-operated over its left-hand winding by way of earth, armatures b3 and M71, left-hand winding of relay HA, contacts NR3, armature 04 to battery via the lower winding of relay C in series with the vertical magnet. The incoming speaking leads are at the same time switch-ed through to the upper set of negative and positive wipers by Way of armatures c5, c6, hb4, M13 and ha l.

In case both test wipers encounter free outlets, both test relays HA and HB restore whereupon relay C is re-energised as above and re-operates relay HA to switch the connection through over the upper set of wipers. Priority is therefore always given to the upper set of wipers in these circumstances.

If all the outlets in the level selected prove busy, the wipers are rotated to the 11th position where the cam springs S are mechanically operated. Relays HA and HB release since there is no earth potential encountered by the PI and P2 wipers and cause the energisation of relay C in the usual manner. Relay HA is then reoperated to switch the upper set of wipers through to the 11th step cam contacts which are multipled together and which connect with the winding of relay A. The latter relay remains held in a manner to be described and hence relays B, C and HA also remain operated. Cam contacts SI and S3 connect relay A in circuit with the busy flash and tone cam assemblies BF and BT while contacts S2 extend an earth over the test wiper PI to operate an overflow meter which may be connected to the 11th outlet of that particular level for traflic observation purposes. During the time cam contacts BT are closed the primary of the busy tone transformer is connected up and busy tone is therefore supplied to the middle winding of relay A over the secondary circuit by way of common conductor I3; hence busy tone is returned to the calling subscriber in a balanced circuit by induction irom the middle to the outer windings of relay A. During the application of the tone, the cam assembly BF supplies an earth which short circuits the centre winding of relay A which however now holds over its two outer windings in series with the calling loop. During the transit time of cam springs BF relay A is arranged to hold over its three windings in series. On disconnection of the tone by the cam contacts ET the contacts BF connect a resistance battery to common lead I4 in order to flash the supervisory lamp if the call has been set up by an operator. Whilst this flash battery is being applied to the line the outer windings of relay A are short-circuited but the relay continues to hold over its middle winding from the flash battery through the earthed busy tone transformer.

Upon the release of the connection at the end of conversation earth is removed from the release trunk conductor P and relay HA or relay HB as the case may be releases. At armatures full or hbl, relay C is now de-energised and again complates a self-interrupted driving circuit for the rotary magnet RM from earth supplied to common conductor II by way of equipment which is arranged to give a delayed alarm in case of failure to release, test jack T, armatures b2 and 03, interrupter contacts rm, contacts N l, armature c2, magnet RM to battery. Accordingly the wipers are rotated clear of the banks after which they fall and rotate beneath the banks under spring tension back to their normal positions where the off-normal contacts N i open and disconnect the homing circuit. Preferably the rotary magnet is mechanically prevented from opening its interrupter contacts. during the release movement so that there is no tendency for it to chatter,

At the commencement of release an initial unguard period on the incoming P conductor represented by the sum of release times of relays I-IA or HB and relay C, is provided to enable preceding switches to restore. On release of relay C following the release of either relay HA or HR, earth will be extended by way of armature cl, springs N2 and armature hbl on to the P conductor to guard against premature seizure dur ing release. When the switch reaches normal, contacts N2 open and remove the guarding earth thus freeing the switch for further use.

A test buzzer wired to the test jack T by way of conductor l0 and armature hbt enables the set of wipers in use to be determined without removing the dust cover from the switch.

It will be appreciated that with the circuit shown if the "make-before-break contacts of relay A should remain together for an appreciable time due to the initial energisation of the relay over a long or leaky line, there is no danger of a preliminary pulse being sent to the vertical magnet since relay B will be short-circuited at armature at and hence relay C will not yet be operated.

It will be understood that the invention is not limited to a group selector but is equally applicable to a final selector or other switch responding to impulses.

We claim:

1. In a telephone system, a line relay, a second relay, a source of battery potential, a unidirectional rectifier unit, means controlled by the energization of said line relay for completing and energizing circuit for said second relay, means controlled responsive to the energization of said second relay for completing a locking circuit for itself exclusive of said line relay controlled means, said energizing and locking circuits including in series said second relay, said rectifier unit, and said source of potential, and circuit connections such that said second relay is shunted by said line relay when the latter deenergizes.

2. In an automatic switch, an operating magnet, said magnet having one of its terminals connected to negative exchange battery, a rectifier unit, a guard relay, said guard relay having one of its terminals connected in series with said rectifier and said negative exchange battery and 3. In a telephone system, an automatic switch,

a line relay, a guard relay, a control relay, and an operating magnet for said switch, a first circuit including said control relay and said magnet in series, a non-inductive battery feed circuit, means controlled by the energization of said line relay for energizing said guard relay in series with said non-inductive battery deed circuit, means controlled by the energization of said guard relay for energizing said control relay,

means controlled by the deenergization of said line relay for shunting said guard relay from said non-inductive battery feed circuit and for completing said first circuit in parallel with said non-inductive battery feed circuit to energize said magnet, said non-inductive battery feed circuit including a rectifier unit poled to prevent said non-battery feed circuit from shunting said first circuit when said line relay deenergizes.

4. In an automatic switch, a line relay having front and back contacts, a guard relay, a control relay, a circuit for energizing said guard relay closed at said front contacts responsive to the first energization of said line relay, means controlled by the energization of said guard relay for completing a locking circuit for itself independent of said front contacts and for complet ing an energizing circuit for said control relay, an operating magnet, means controlled by the energization of said control relay for preparing ,1

a circuit for said magnet and for rendering the circuit through the said front contacts ineffective, and a shunting circuit for rendering said guard relay slow to release and simultaneously completing an energizing circuit for said magnet closed at said back contacts each time said line relay deenergizes.

5. In a telephone system, an automatic switch, an operating magnet therefor, a line relay for controlling said magnet, a guard relay, a control relay, a first circuit for transmitting an impulse of current to energize said guard relay closed on the first energization of said line relay, means controlled by the energization of said guard relay for locking itself in said energized position and for energizing said control relay, means controlled by the energization of said control relay for preparing a circuit for said magnet and for disconnecting said first circuit, and means. controlled each time said line relay deenergizes for shunting said guard relay to make it slow acting and for simultaneously energizing said magnet.

REGINALD TAYLOR. GEORGE THOMAS BAKER. 

